Historically, integrated circuits have been flat and rigid, but the current development of “flexible electronics” envisions rollable displays and wearable electronics, and promises to revolutionize our daily lives. (S. R. Forrest, Nature 2004, 428, 911; A. L. Briseno, S. C. B. Mannsfeld, M. M. Ling, S. H. Liu, R. J. Tseng, C. Reese, M. E. Roberts, Y. Yang, F. Wudl, Z. N. Bao, Nature 2006, 444, 913; J. H. Ahn, H. S. Kim, K. J. Lee, S. Jeon, S. J. Kang, Y. G. Sun, R. G. Nuzzo, J. A. Rogers, Science 2006, 314, 1754; D. Y. Khang, H. Q. Jiang, Y. Huang, J. A. Rogers, Science 2006, 311, 208; and L. Groenendaal, G. Zotti, P. H. Aubert, S. M. Waybright, J. R. Reynolds, Advanced Materials 2003, 15, 855.) Thanks to the explosive improvement in the performance of devices made from organic materials in recent years, conjugated organic materials are regarded as one of the most promising candidates for commercializable flexible electronics. (A. L. Briseno, S. C. B. Mannsfeld, M. M. Ling, S. H. Liu, R. J. Tseng, C. Reese, M. E. Roberts, Y. Yang, F. Wudi, Z. N. Bao, Nature 2006, 444, 913; and Y. R. Sun, N. C. Giebink, H. Kanno, B. W. Ma, M. E. Thompson, S. R. Forrest, Nature 2006, 440, 908.) Current efforts are mainly focused on increasing the performance of devices and the density of integration of the devices for high-end electronic applications. (D. Y. Khang, H. Q. Jiang, Y. Huang, J. A. Rogers, Science 2006, 311, 208.)
Patterning is essential for the fabrication of the integrated circuitry. Special attention must be paid to conducting polymer processes because the organic layers must retain their own electronic properties after the patterning process. For this purpose, various modified methods for patterning of conducting polymer have been devised. (Holdcroft, S. Advanced Materials 2001, 13, 1753-1765.) For example, in the electrooxidative deposition of conjugated polymers (such as polypyrrole and polyaniline) on a surface, a pre-patterned metal layer was been used for electropolymerization and a pre-patterned oxidizing agent layer was applied to oxidative polymerization of conducting polymer. (Sayre, C. N. & Collard, D. M. Langmuir 1997, 13, 714-722; Collard, D. M. & Sayre, C. N. Synthetic Metals 1997, 84, 329-332; Sayre, C. N. & Collard, D. M. Journal of Materials Chemistry 1997, 7, 909-912; Li, Z. F. & Ruckenstein, E. Macromolecules 2002, 35, 9506-9512; and Ruckenstein, E. & Li, Z. F. Advances in Colloid and Interface Science 2005, 113, 43-63.) In addition, photo-sensitive precursor polymer films have been selectively developed by irradiation and then subsequently converted to patterned conducting polymer. (Renak, M. L., Bazan, G. C. & Roitman, D. Advanced Materials 1997, 9, 392-395. Further, physical patterning method of ink-jet printing, screen printing, and soft lithography technique have also been used for micron-size pattern of conducting polymer. Recently, the use of near-field optical lithography of a conjugated polymer was reported, whose resolution can reach 160 nm. (Sirringhaus, H. et al. Science 2000, 290, 2123-2126; Bao, Z. N., Feng, Y., Dodabalapur, A., Raju, V. R. & Lovinger, A. J. Chemistry of Materials 1997, 9, 1299; Rogers, J. A. et al. Proceedings of the National Academy of Sciences of the United States of America 2001, 98, 4835-4840; Richards, D. & Cacialli, F. Philosophical Transactions of the Royal Society of London Series A—Mathematical Physical and Engineering Sciences 2004, 362, 771-786; and Riehn, R., Charas, A., Morgado, J. & Cacialli, F. Applied Physics Letters 2003, 82, 526-528.)
However, although current lithographic techniques for inorganic semiconductor chips produce feature sizes as small as a few tens of nanometers, most if not all of these techniques are incompatible with organic materials. (J. A. DeFranco, B. S. Schmidt, M. Lipson, G. G. Malliaras, Organic Electronics 2006, 7, 22.) For example, organic substrates can be damaged by wet chemical treatments and are vulnerable to mechanical stress from the patterning process. These constraints demand either the modification of photolithography or newly devised schemes applicable to organic materials. (J. A. DeFranco, B. S. Schmidt, M. Lipson, G. G. Malliaras, Organic Electronics 2006, 7, 22; and C. D. Muller, A. Falcou, N. Reckefuss, M. Rojahn, V. Wiederhirn, P. Rudati, H. Frohne, O. Nuyken, H. Becker, K. Meerholz, Nature 2003, 421, 829.) However, the performance of these circumvented strategies is still far from that of current photolithographic techniques in terms of minimum feature size, reliability, and throughput of patterning. (S. Holdcroft, Advanced Materials 2001, 13, 1753.) The ability to produce dense patterns of sub-micron features over the entire area of the substrate is limited by insufficient adhesion which results in mechanical failures, such as cracks, displacements, and delaminations. (J. A. DeFranco, B. S. Schmidt, M. Lipson, G. G. Malliaras, Organic Electronics 2006, 7, 22.)
Moreover, for maximized durability and reliability of flexible electronic devices, mechanical robustness is extremely important, requiring excellent interfacial properties and adhesion between the conductive thin film and flexible polymeric substrates. (Y. Leterrier, L. Medico, F. Demarco, J. A. E. Manson, U. Betz, M. F. Escola, M. K. Olsson, F. Atamny, Thin Solid Films 2004, 460, 156.) Transparent conducting oxides (TCOs), such as indium tin oxide (ITO), which are usually used as anode materials in organic electronics, are inherently brittle, which limits their applications in flexible electronics. (Z. Chen, B. Cotterell, W. Wang, Engineering Fracture Mechanics 2002, 69, 597.) Conducting polymer films regarded as alternatives to TCOs are weakly physisorbed on substrates, and are also vulnerable to the delamination from the substrates with repeated flexing. (G. P. Crawford, Flexible flat panel displays, John Wiley & Sons, Hoboken, N.J., 2005.) Covalent bonding of conducting polymer films to substrates can prevent delamination.
In spite of its engineering significance, only a few reports address grafting of conducting polymers. For example, Ruckenstein and Li have reported a conducting polyaniline film grafted on glass plates using a silane coupling agent. (Li, Z. F. & Ruckenstein, E. Synthetic Metals 2002, 129, 73-83; Li, Z. F. & Ruckenstein, E. Macromolecules 2002, 35, 9506-9512; and Ruckenstein, E. & Li, Z. F. Advances in Colloid and Interface Science 2005, 113, 43-63.) A similar approach was also performed for grafted poly (3-hexylthiophene) (P3HT) on Si wafer. (Liu, C. J., Oshima, K., Shimomura, M. & Miyauchi, S. Journal of Applied Polymer Science 2006, 100, 1881-1888.) It has further been shown that grafted poly pyrrole can also be obtained on various metal and metal oxide surfaces using phosphonic acids. (Oberoi, S., Jahne, E. & Adler, H. J. P. Macromolecular Symposia 2004, 217, 147-159.) However, these methods require tedious stepwise reactions to attach linkers for further grafting of conducting polymer. Further, while precursor polymers have been used for grafting of conducting polymer using post-functionalization, the grafting was not confined to the surface. (Bhattacharya, A. & Misra, B. N. Progress in Polymer Science 2004, 29, 767-814.